Twenty-three million surgical procedures are performed annually in the United States, requiring healing of injured tissues or wounds. Failure of wound healing contributes to morbidity, mortality and increased health care costs resulting from longer hospital stay and increased costs of treatment. Beyond techniques to limit wound infection, the promotion of healing and recovery after surgery are believed to be improved by early postoperative activity. The effect of physical activity on wound healing and variables that are critical to repair, blood flow and oxygen levels in peripheral tissues has not been determined. A better understanding of how physical activity effects these factors will guide development of clinical activity programs that promote optimal wound healing and recovery from surgery. The specific aims of this study are to 1) determine if augmented postoperative activity enhances wound healing as measured by cellular and subcellular markers of healing, 2) describe the effect of augmented activity on subcutaneous oxygen (PscO2) and blood flow and, 3) describe the relationships between subcutaneous perfusion/oxygen and cellular markers of healing. Using a randomized, two group experimental design subjects scheduled for total hip arthroplasty will participate in either conventional postoperative activity (n=28) or a 5 day augmented postoperative activity protocol (n=28). Wound healing will be evaluated by analysis of tissue cellularity, mRNA for pro alpha1[I] collagen and hydroxyproline from a tissue sample obtained from a small, polytetrafluoroethylene tube placed subcutaneously and removed on the 7th postoperative day. PscO2 and blood flow will be measured on the day of surgery and the next two postoperative days with an optode/tonometer system. Differences between groups on healing, tissue oxygen and perfusion variables will be tested with Student's t test, ANOVA for repeated measures, or the Mann Whitney U test depending on the level of measurement. Relationships will be tested with Pearson's product moment or Spearman's rank correlation coefficients.